The present invention generally relates to an apparatus and a method for etching a glass panel and more particularly, relates to an apparatus and a method for etching a plurality of glass panels on both sides of the panel simultaneously with improved thickness uniformity for fabricating thin glass panels used in liquid crystal displays.
Liquid crystal display devices have been used for many years. In the beginning, their uses have been concentrated in small appliance applications such as electronic watches and calculators. LCD""s are now used in applications for instrument panel numerical displays and graphical displays. Advantages presented by LCD""s are their inherent properties of small thickness, lightweight, low driving voltage requirement and low power consumption. As a consequence, more recent applications of color LCD""s can be found in small screen television sets, notebook computer display panels and video camera viewfinders as replacements for conventional CRT""s.
A liquid crystal display device can be made either a color unit or a black and white unit. The device may also be constructed as a reflective-type or as a transmittive type, depending on the light source used. Since liquid crystal molecules respond to an externally applied electrical voltage, liquid crystals can be used as an optical switch or as a light valve.
A liquid crystal display cell is a single pixel that is constructed by two parallel glass plates, i.e. an upper glass plate and a lower glass plate. Both the upper plate and the lower plate have a polarizing film coated on its outer surface. A cavity formed between the two plates is filled with a liquid crystal material. One of the most commonly used liquid crystal material is of the twisted hematic (TN) type wherein the term twist refers to the tendency of the liquid crystal to form chains that rotate from one side of the gap between the plates to the other side of the gap. The degree of rotation can be controlled during the fabrication process.
When a light beam passes through the polarizer and the liquid crystal display cell, its polarization direction is rotated by following the physical rotation of the liquid crystal molecules. The polarizer on the exit side of the liquid crystal cell may be positioned such that it allows a rotated light beam to pass through the polarizer. When viewed from the side of the polarizer, the pixel or the liquid crystal cell thus appears clear, i.e. in a transmitting mode.
A transmitting electrical conductor such as indium-tin-oxide (ITO) is normally deposited on the inner surfaces of the glass plates. The transparent electrical conductor layer may be patterned into a series of mutually perpendicular lines. When a voltage is applied across the cell cavity by addressing the appropriate line on each side of the cell, liquid crystal molecules reorient themselves to follow the applied electrical field. The liquid crystal materials thus become untwisted. The passage of the untwisted light beam is blocked by the exit polarizer as long as the voltage is present. When the voltage is turned off the liquid crystal molecules return to their original state and the cell or the pixel becomes clear again. As previously described, typical voltages and currents required to activate the liquid crystal molecules are relatively low making it an ideal candidate for incorporation in a battery-operated equipment where low power consumption is essential. A typical twisted hematic (TN) liquid crystal cell used for small displays have a twist angle of 90xc2x0. More recently developed supertwisted nematic (STN) material forms a twist angle up to 270xc2x0 and thus allow higher contrast so that many pixel elements can be multiplexed in a single display.
While the liquid crystal display device described above is the transmittive type, liquid crystal display devices of the reflective-type are also used. In a reflective-type liquid crystal device, one of the upper plate and the lower plate is replaced by a reflector plate which is light reflective and not transmittive. The reflector plate may be fabricated of a glass substrate with transistors or other active components built on top and coated with a metal reflective layer. In the reflective-type liquid crystal display device, the light source for illuminating the liquid crystal display is from the ambient such that a display is viewed in a reflective manner.
One of the characteristics for the reflective-type liquid crystal display device is the noise signals reflected from the top or the cover glass plate of the display device. In a conventional reflective-type liquid crystal display device, the reflector plate and the top cover plate are parallel to each other. When an outside light source is used to produce an image in the liquid crystal device under the reflective principal, the light reflected from the reflector plate and from the top plate have the same reflective angle. Since the light reflected from the top cover plate does not produce the image formed in the liquid crystal display, only noise signals are produced which decrease the contrast of the display device. Furthermore, the noise/signal ratio of the device is also increased which affects the quality of images produced by the display device.
For an LCD to be effectively utilized in applications of portable electronics, i.e. such as portable televisions and notebook computers, an important factor to be considered is the reduction of size and weight of the LCD unit. Since the driving circuit and the thin film transistors utilized on a LCD unit are the necessary elements and are already formed in a miniature scale that any further reductions in size and weight in these elements is not likely. The only possible element in the LCD unit to target a weight reduction is the glass substrate. Since proportionally the glass substrate is a heavy element in the LCD unit, methods for reducing the weight of the glass substrate have been the subject of investigation in the LCD industry.
To reduce the weight of a glass substrate, an obvious approach is to reduce its thickness. However, the thinning process of the glass substrate is difficult to carry out since thin glass can be easily damaged due to the reduction in mechanical strength and furthermore, the thinning process may cause surface roughness which directly effects the image quality of a LCD unit.
FIG. 1 is a graph illustrating U.S. Pat. No. 5,989,450 issued to Kim disclosing an etchant for etching glass substrates. In the method, an etchant solution that contains HF in water at a concentration of at least 5 vol. % and an alcohol such as ethanol, methanol, propanol, butanol and isopropyl alcohol to a concentration of about 5 vol. % is held in container 12. A porous plate 14 generates bubbles 8 for separating the etch residue and particles from the surface of the glass substrate 21. While the etch residue is more easily removed by the etchant that contains 5 vol. % alcohol, the method cannot achieve uniform etching on a large glass substrate, and furthermore, cannot be used to etch glass substrates that already have conductive elements formed in an edge portion of the substrate.
Another method, as shown in FIG. 2 and disclosed by U.S. Pat. No. 6,071,374 to Kim, illustrates an apparatus for etching a glass substrate which includes a first bath 13 containing an etchant, at least one porous panel 15 that has a plurality of jet holes 16 in the first bath, the porous panel contains the etchant to jet the etchant against the glass substrate 30. A container 20 stores the etchant, and a pump 24 is used to supply the etchant from the container to the porous panel 15 by a connection between the pump, the container and the porous panel.
As shown in FIG. 2, the glass substrates 30 are fixed by at least a pair of projections 19 formed on a stand 18 and arranged between the porous panels 15. When the pump 24 is operating, the etchant is sprayed onto the glass substrate 30 through the jet holes 16 by the pressure of the pump. An inner bath 13 also contains the etchant. When the etchant in the storage container 20 is supplied to the stand 18 through the etchant supplying pipe 25 by the operation of the pump 24, the pressure of the pump 24 is transmitted to the etchant of the porous panel 15 connected to the stand 18. The etchant is thus sprayed onto both sides of the glass substrate 30 through the jet hole 16. A plurality of jet holes 16 are also provided in the porous panels 16 in the vertical and horizontal directions to spray the etchant onto the glass substrate 30. The bubbles are generated from the gas supplied from a gas tank 26 through a gas supplying pipe 27. While the set-up shown in FIG. 2 improves the uniformity of etching when compared to the set-up shown in FIG. 1, there are still numerous drawbacks to the method such as the difficulty in controlling a spray of the etchant through the jet holes 16 and that the method can only be used to etch a plain glass substrate, i.e. not a glass panel that has conductive elements formed on top. There is no provision in the apparatus to protect any conductive elements that may have been formed on the glass panel.
It is therefore an object of the present invention to provide an apparatus for etching a plurality of glass panels that does not have the drawbacks or the shortcomings of the conventional apparatus.
It is another object of the present invention to provide an apparatus for etching a plurality of glass panels capable of producing more uniform thickness control on the panels.
It is a further object of the present invention to provide an apparatus for etching a plurality of glass panels that is capable of producing improved planarity across the surface of the panels.
It is another further object of the present invention to provide an apparatus for etching a plurality of glass panels which includes a rotatable panel holder for holding the panels and for rotating the panels in an etchant solution.
It is still another object of the present invention to provide an apparatus for etching a plurality of glass panels that includes a panel holder capable of shielding conductive elements formed on the panels from being exposed to an etchant solution.
It is yet another object of the present invention to provide a method for etching a plurality of glass panels by rotating a panel holder holding a plurality of panels immersed in a volume of etchant at a pre-determined rotational speed.
It is still another further object of the present invention to provide a method for etching a plurality of glass panels by oscillating the panels in opposite rotational directions.
It is yet another further object of the present invention to provide a method for etching a plurality of glass panels by rotating the panels immersed in an etchant solution at a speed between about 5 rpm and about 60 rpm.
In accordance with the present invention, an apparatus and a method for etching a plurality of glass panels with improved uniformity and thickness control are provided.
In a preferred embodiment, an apparatus for etching a plurality of glass panels is provided which includes a panel holder of cubicle shape formed of two sidewalls, a bottom wall and a back wall for holding a plurality of glass panels vertically therein, the holder may have an open top and an open front each engaged by a frictional bar for frictionally engaging a first and a second adjacent edges of each of the plurality of glass panels, the back wall and the bottom wall each being further provided with a plurality of tracks for frictionally engaging a third and a fourth adjacent edges of each of the plurality of glass panels, the two side walls being provided with connecting means for connecting to a rotating means provided in a tank into which the holder is positioned; and a tank that has a cavity for holding a volume of an etchant solution and the panel holder immersed in the volume of etchant solution, the tank is further provided with support means and rotating means for supporting and rotating the panel holder in a plane of the plurality of glass panels to a predetermined rotational speed.
In the apparatus for etching a plurality of glass panels, the tank may optionally include means for circulating the etchant solution. The panel holder may be formed of two side walls and a bottom wall with the top, the front and the back of the holder open. The open top, open front and the open back each may be engaged by a frictional bar for frictionally engaging a first, a second and a third adjacent edge of each of the plurality of glass panels. The plurality of tracks may be formed of a material that has sufficient elasticity for providing frictional engagement, or formed of an elongated block that has a recessed slot therein for seating the third and the fourth adjacent edges of each of the plurality of glass panels. The plurality of tracks may still further be formed of an elongated, elastomeric block that has a recessed slot therein for receiving an edge of one of the plurality of panels, or formed to a height sufficient to shield conductive leads formed on an edge portion of the glass panel. The support means may further include a shaft and a bearing for rotating the shaft. The rotating means may include an electric motor.
The present invention is further directed toward a method for etching a plurality of glass panels that includes the operating steps of first providing a panel holder for holding a plurality of glass panels; positioning a plurality of glass panels vertically spaced-apart in the panel holder; mounting the panel holder in an etch tank; filling the etch tank with a volume of etchant immersing the plurality of glass panels; and rotating the panel holder in a plane of the plurality of panels at a pre-determined rotational speed.
The method for etching a plurality of glass panels may further include the step of providing a panel holder in a cubicle shape that has at least two open sides and exposing the plurality of glass panels to the volume of etchant. The method may further include the step of positioning the plurality of glass panels vertically in the panel holder with each panel frictionally engaged on at least one edge by a frictional engagement means. The method may further include the step of providing the frictional engagement means in a track that has a recessed slot therein, or providing the frictional engagement means fabricated of an elastomeric material. The method may further include the step of holding the plurality of glass panels in place during -the rotation by at least one frictional bar mounted on each of the open sides by engaging an edge of the plurality of panels. The method may further include the step of rotating the panel holder alternatingly in opposite directions in an oscillating mode, or rotating the panel at a rotational speed between about 5 rpm and about 60 rpm. The method may further include the step of providing the volume of etchant in a diluted solution of HF having a concentration of at least 5 vol. %, or the step of immersing the plurality of glass panels in the volume of etchant while being rotated for a time period of at least 3 min.